PMOS Finfet

ABSTRACT

A method for fabricating a semiconductor device includes forming a doped semiconductor layer on a substrate and forming a fin structure disposed on the doped semiconductor layer. The fin structure is doped with a p-type dopant. The method further includes forming a source/drain region within an upper portion of the fin structure and forming a fin sidewall along a lower portion of the fin structure. The fin sidewall has the p-type dopant.

PRIORITY INFORMATION

This application is a divisional of U.S. patent application Ser. No.15/460,006, filed Mar. 15, 2017, and entitled “Improved PMOS FinFET,”which claims the benefit of U.S. Provisional Application No. 62/435,014filed Dec. 15, 2016, and entitled “Improved PMOS FinFET,” thedisclosures of which are hereby incorporated by reference in theentirety.

BACKGROUND

In the semiconductor integrated circuit (IC) industry, technologicaladvances in IC materials and design have produced generations of ICswhere each generation has smaller and more complex circuits than theprevious generation. In the course of IC evolution, functional density(i.e., the number of interconnected devices per chip area) has generallyincreased while geometry size (i.e., the smallest component (or line)that can be created using a fabrication process) has decreased. Thisscaling down process generally provides benefits by increasingproduction efficiency and lowering associated costs. Such scaling downhas also increased the complexity of IC processing and manufacturing.

One type of semiconductor device that can be fabricated is a Fin FieldEffect Transistor (FinFET). In a FinFET, a fin-shaped semiconductorstructure is formed on a substrate. A gate device that wraps around thefin structure can then be formed. Additionally, active regions such assource/drain regions are then formed within the fin structure adjacentthe gate structure. The gate device and adjacent source/drain regionsthus form a transistor with the channel extending through the finstructure underneath the gate. FinFET devices include both p-type (PMOS)transistors and n-type (NMOS) transistors. PMOS devices utilize holes ascharge carries while NMOS devices utilize electrons as charge carriers.Due to the characteristic different between PMOS and NMOS transistors,there are different design considerations for each type of transistor.It is desirable to improve the efficiency and performance of finFETtransistors.

BRIEF DESCRIPTION OF THE DRAWINGS

Aspects of the present disclosure are best understood from the followingdetailed description when read with the accompanying figures. It isnoted that, in accordance with the standard practice in the industry,various features are not drawn to scale. In fact, the dimensions of thevarious features may be arbitrarily increased or reduced for clarity ofdiscussion.

FIGS. 1A, 1B, 1C, 1D, 1E, 1F, 1G, 1H, 1I, and 1J are diagrams showing anillustrative process for forming an improved PMOS FinFET device,according to one example of principles described herein.

FIG. 2 is a diagram showing various characteristics of an improved PMOSFinFET device, according to one example of principles described herein.

FIG. 3 is a flowchart showing an illustrative method for forming animproved PMOS FinFET device, according to one example of principlesdescribed herein.

DETAILED DESCRIPTION

The following disclosure provides many different embodiments, orexamples, for implementing different features of the provided subjectmatter. Specific examples of components and arrangements are describedbelow to simplify the present disclosure. These are, of course, merelyexamples and are not intended to be limiting. For example, the formationof a first feature over or on a second feature in the description thatfollows may include embodiments in which the first and second featuresare formed in direct contact, and may also include embodiments in whichadditional features may be formed between the first and second features,such that the first and second features may not be in direct contact. Inaddition, the present disclosure may repeat reference numerals and/orletters in the various examples. This repetition is for the purpose ofsimplicity and clarity and does not in itself dictate a relationshipbetween the various embodiments and/or configurations discussed.

Further, spatially relative terms, such as “beneath,” “below,” “lower,”“above,” “upper” and the like, may be used herein for ease ofdescription to describe one element or feature's relationship to anotherelement(s) or feature(s) as illustrated in the figures. The spatiallyrelative terms are intended to encompass different orientations of thedevice in use or operation in addition to the orientation depicted inthe figures. The apparatus may be otherwise oriented (rotated 90 degreesor at other orientations) and the spatially relative descriptors usedherein may likewise be interpreted accordingly.

As described above, it is desirable to improve the efficiency andperformance of finFET transistors. According to the present example, aPMOS finFET device includes a fin structure disposed on a semiconductorsubstrate. The fin structure includes a fin sidewall that is partiallyremoved so as to expose the upper portion of the fin. The fin structurefurther includes source/drain features that are formed into the finstructure. The source/drain features extend about halfway through theheight of the fin structure. Additionally, the top portion of the finsidewall corresponds with the bottom surface of the source/drainfeatures. Both the fin structure and the source/drain regions mayinclude silicon germanium that is doped with a p-type dopant such asboron. The source/drain regions may have a higher concentration ofgermanium than the channel regions.

FIGS. 1A, 1B, 1C, 1D, 1E, 1F, 1G, and 1H are diagrams showing anillustrative process for forming an improved PMOS FinFET device. FIG. 1Aillustrates a substrate 102 with an n-well 104 and a p-well 106 formedtherein. A semiconductor layer 108 is disposed on top of the n-well 104and the p-well 106.

The substrate 102 may be a semiconductor wafer comprising silicon. Thesemiconductor wafer may be a standard wafer used in semiconductorfabrication processes. For example, the semiconductor wafer may be around wafer having a diameter of about 300 millimeters.

The n-well 104 and the p-well 106 may be formed by doping thesemiconductor with the appropriate type of dopant. For example, to formthe n-well, the portions of the semiconductor substrate that are to bep-wells are covered by a mask such as an oxide material. Then, a dopingprocess such as an implanting process can be applied to the exposedportions of the semiconductor substrate. The n-well may be doped with ann-type dopant such as Arsenic.

After the n-well regions 104 are formed, the n-well regions may becovered with a mask material that is then patterned to expose theportions of the substrate where the p-wells 106 are to be formed. Then,a doping process such as an implanting process may be used to dope theexposed portions of the semiconductor substrate 102 with a p-type dopantsuch as boron. In some examples, the p-wells 106 may be formed beforethe n-wells.

The semiconductor layer 108 may be formed by use of an epitaxial growthprocess. An epitaxial growth process is one in which semiconductormaterial is provided through a carrier gas and is deposited into acrystal structure onto the underlying crystal substrate. Thus, thesemiconductor layer gets deposited onto the semiconductor n-wells 104and p-wells 106. In one example, the semiconductor layer 108 may besilicon. The semiconductor layer 108 may be selected for use as a finstructure for an NMOS device. Thus, the semiconductor layer 108 may alsobe referred to as an NMOS semiconductor layer 108.

FIG. 1B illustrates the portions of the semiconductor layer 108 over then-wells 104 removed and replaced with a semiconductor layer 112 selectedfor use in the fin structure of a PMOS device. Thus, the semiconductorlayer 112 may also be referred to as a PMOS semiconductor layer 112.

To form the PMOS semiconductor layer 112, the portions of the NMOSsemiconductor layer 108 that are over the p-wells 106 are covered with amask layer. The mask layer is patterned to expose the regions over then-wells 104. Then an etching process is applied to remove thesemiconductor layer 108 that is exposed through the mask. In someexamples, and as illustrated, the semiconductor layer 108 is notentirely removed. Instead, a small, thin layer is left remaining to be aseed layer 110. The seed layer 110 may reduce the number of defects thatare present in the PMOS semiconductor layer 112. The PMOS semiconductorlayer 112 may be formed through an epitaxial growth process. In someexamples, a Chemical Mechanical Planarization (CMP) process may be usedto planarize the top surface of the PMOS semiconductor layer 112 and theNMOS semiconductor layer 108. A CMP process includes a mechanicalcomponent and a chemical component. The mechanical component involvesabrasive particles and the chemical component involves a chemicaletchant.

In one example, the PMOS semiconductor layer 112 may include silicongermanium (SiGe). Other types of semiconductor materials that arewell-suited for PMOS transistors may be used. The silicon germanium mayhave a concentration of germanium within a range of about 25 to 40%.

FIG. 1C illustrates formation of the fin structures and Shallow TrenchIsolation (STI) structures. To form the fin structures, the substrate ispatterned using photolithographic techniques. For example, a photoresistmaterial may be deposited and patterned. Patterning the photoresist maybe done by exposing the deposited photoresist to a light source througha mask. The photoresist layer may then be developed to expose regionsthat are to be etched. An etching process is then applied to removeportions of the substrate to form the fin structures 111 as shown.

After the fin structures are formed, STI structures 114 may be formedbetween the fin structures 111. This may be done by depositing adielectric material and etching that material to the desired height. Thedielectric material and the material of the fin structures may beselected so that the dielectric material of the STI structures can beremoved while leaving the fin structures 111 substantially intact.

FIG. 1D illustrates deposition of a fin sidewall 116. The fin sidewall116 may be deposited through use of a deposition process such as aChemical Vapor Deposition (CVD) process. Other deposition processes maybe used to deposit the fin sidewall 116. The fin sidewall 116 mayinclude a dielectric material such as a nitride material.

FIG. 1E illustrates a doping process 118 to dope the PMOS fin structures111 with a p-type dopant such as boron. Before the doping process 118 isapplied, the NMOS features may be covered. The doping process 118 alsointroduces the p-type dopant into the fin sidewall 116. In someexamples, the doping process 118 may be a plasma doping process. Aplasma doping process involves using a high voltage direct current (DC)to extract ions from plasma and inject them into a target. For example,a plasma gas may include p-type dopants such as boron. Such a plasma gasmay then be introduced into a chamber that also includes the substrate.An electromagnetic field can then be applied to direct ions from theplasma into the surface.

FIG. 1F illustrates an etching process 120 to remove the fin sidewallfrom an upper portion of the PMOS fin structures 111. The etchingprocess may be an anisotropic process such as a dry etching process. Adry etching process involves directing ions at a substrate to removematerial from that substrate. A dry etching process can be selective soas to remove some type of materials while leaving other types ofmaterials substantially intact. Thus, the etching process 120 can removethe fin sidewalls 116 while leaving the PMOS fin structures 111substantially intact. The etching process 120 may be applied until thetop surfaces of the fin sidewalls are at a point that is within themiddle of the height of the fin structures 111. In some examples, theetching process 120 may be applied until the top surfaces of the finsidewalls 116 are about halfway between the top surface and bottomsurface of the PMOS fin structures 111. As will be described in moredetail below, the top surface of the etched fin sidewalls 116 maycorrespond with the bottom of the source/drain features that are formedin the PMOS fin structures 111.

FIG. 1G is a diagram illustrating another doping process 122 tointroduce dopants into the PMOS fin structures 111. The doping process122 may be similar to the doping process 118 described above. In someexamples, the doping process 118 may be performed and the doping process122 may be omitted. In some examples, the doping process 118 may beomitted and the doping process 122 may be performed. In some examples,both the doping process 118 and the doping process 122 may be performed.

FIG. 1H illustrates a diagram of a semiconductor device along a vieworthogonal to the view shown in FIGS. 1A-1G. Specifically, FIG. 1Hillustrates a gate structure 126 having sidewalls 128 formed thereon fora transistor. The gate structure 126 may be formed before the finsidewalls 116 are formed. The gate structure 126 may be formed in one ofa variety of manners. In one example, a conductive material, such aspolysilicon is deposited onto the substrate. The polysilicon layer isthen patterned to create elongated gate structures 126 that wrap aroundthe fin structures 111. After the gate structure is formed, and beforesource/drain regions are formed, the gate sidewalls 128 may be depositedonto the sidewalls of the gate structure. The gate sidewalls 128 may bea dielectric material.

FIGS. 1I and 1J illustrate formation of source/drain regions 124 on bothsides of the gate structure to form a transistor 140. FIG. 1I is across-section along the same cross-section illustrated in FIGS. 1A-1G.The channel region 130 is positioned underneath the gate structure 126and between the source/drain regions 124.

The source/drain regions 124 may be formed by etching portions of thefin structure to create a cavity within the fin structures. The etchingprocess may be designed so as to create the cavity at a specific depthwithin the fin structures 111. For example, and as illustrated, thecavity may have a depth that extends about halfway through the height ofthe fin structures 111. After the cavity is formed, an epitaxial growthprocess may be applied to epitaxially grow the source/drain regions 124within the cavities. The source/drain regions 124 may also be doped insitu. In other words, the source/drain regions 124 may be implanted withthe desired dopant species while the source/drain regions 124 are beingformed.

The source/drain regions 124 may include the same type of semiconductormaterial (e.g., silicon germanium) as the PMOS fin structure 111. Insome examples, however, the source/drain regions may have a largerconcentration of germanium than the PMOS fin structure 111. For example,the source/drain regions 124 may have a concentration of germaniumwithin a range of 45-75 percent. Thus, the source/drain regions 124 mayhave a higher concentration of germanium than the channel region 130 andthe under-region 132.

As illustrated in FIG. 1A, the source/drain 124 regions of adjacent finstructures 111 are merged. In some examples, however, there may be a gapbetween the source/drain regions 124 of adjacent fin structures 111. Inother words, there may be no merging of source/drain regions betweenadjacent fin structures 111.

FIG. 1J illustrates the semiconductor device along a view orthogonal tothe view shown in FIGS. 1A-1G. In other words, FIG. 1J has a similarcross-section to that shown in FIG. 1H. According to one example, thefin structure 111 may have a height 138 within a range of about 50-60nanometers. The thickness 134 of the source/drain region 124 may bewithin a range of about 30-40 nanometers. Similarly, the thickness of136 of the under-region 132 (i.e., the region underneath thesource/drain regions 124) may be within a range of about 25-30nanometers. In other words, the source/drain region 124 extends to apoint that is about halfway between the top and bottom of the finstructure 111. Other heights and thicknesses of the fin structure 111,source/drain regions 124, and under-region 132 are contemplated.

In the present example, the lower portion of the fin structure 111connects with the channel. This adds additional stress on the channel130 and thus improves the carrier mobility through the channel 130.Additionally, the under-region 132 includes the dopant species that isused during the implantation process.

The semiconductor device illustrated in FIGS. 1A-1J are illustrated in amanner so as to convey the principles described herein, and do notnecessarily represent the dimensions of a real semiconductor device thatis fabricated using such principles. For example, while the finstructures are illustrated as substantially rectangular, it isunderstood by one of ordinary skill in the art that real fin structuresmay not necessarily be perfectly rectangular. For example, real finstructures may include rounded corners and slightly non-linear surfaces.Additionally, real fin structures may taper towards a top side of thefin structure.

FIG. 2 is a diagram showing various characteristics of an improved PMOSFinFET device. FIG. 2 illustrates two fin structures 202. The finstructures 202 may be similar to the fin structures 111 described above.The fin structures 202 have a fin sidewall 206 extending from a bottomof the fin structures to a point that is about halfway through theheight of the fin structures 202. The fin sidewalls 206 may be similarto the fin sidewalls 116 described above. Additionally, the source/drainfeatures 204 may extend from the top surfaces of the fin sidewalls 206to a point above the top surfaces 208 of the fin structures.Additionally, the side surfaces 210 of the fin structures 202 may taperinward towards the top of the fin structures. Additionally, the topsurfaces 208 of the fin structures 202 may be rounded.

FIG. 3 is a flowchart showing an illustrative method for forming animproved PMOS FinFET device. According to one example, the method 300includes a process 302 for forming a fin structure 111 on a dopedsemiconductor layer 104. The doped semiconductor layer 104 may be ann-well doped with n-type dopants. The fin structure 111 may include asemiconductor material such as silicon germanium. In one example, thefin structure 111 may be formed by epitaxially growing a layer ofsilicon germanium and patterning that silicon germanium to form the finstructures 111

In some examples, the substrate 102 may be a semiconductor wafercomprising silicon. The semiconductor wafer may be a standard wafer usedin semiconductor fabrication processes. For example, the semiconductorwafer may be a round wafer having a diameter of about 300 millimeters.The n-well 104 and a p-well 106 may be formed by doping thesemiconductor with the appropriate type of dopant. For example, to formthe n-well 104, the portions of the semiconductor substrate 102 that areto be p-wells 106 are covered by a mask such as an oxide material. Then,a doping process such as an implanting process can be applied to theexposed portions of the semiconductor substrate 102. The n-well 104 maybe doped with an n-type dopant such as Arsenic.

After the n-well regions 104 are formed, the n-well regions 104 may becovered with a mask material that is then patterned to expose theportions of the substrate where the p-wells 106 are to be formed. Then,a doping process such as an implanting process may be used to dope theexposed portions of the semiconductor substrate with a p-type dopantsuch as boron. In some examples, the p-wells 106 may be formed beforethe n-wells 104. The semiconductor layer for the PMOS devices may thenbe formed by use of an epitaxial growth process. An epitaxial growthprocess is one in which semiconductor material is provided through acarrier gas and is deposited into a crystal structure onto theunderlying crystal substrate. Thus, the semiconductor layer getsdeposited onto the semiconductor n-wells and p-wells. In one example,the semiconductor layer may be silicon. The semiconductor layer may beselected for use as a fin structure for an NMOS device. Thus, thesemiconductor layer may also be referred to as an NMOS semiconductorlayer.

After the PMOS semiconductor layer is formed, the NMOS semiconductorlayer, which will be patterned to form the fin structures 111, may beformed. Specifically, the portions of the PMOS semiconductor layer overthe n-wells 104 may be removed and replaced with a semiconductor layerselected for use in the fin structure 111 of a PMOS device.

To form the PMOS semiconductor layer, the portions of the NMOSsemiconductor layer that are over the p-wells are covered with a masklayer. The mask layer is patterned to expose the regions over then-wells. Then an etching process is applied to remove the semiconductorlayer that is exposed through the mask. In some examples, and asillustrated, the semiconductor layer is not entirely removed. Instead, asmall, thin layer is left remaining to be a seed layer. The seed layermay reduce the number of defects that are present in the PMOSsemiconductor layer. The PMOS semiconductor layer may be formed throughan epitaxial growth process. In some examples, a Chemical MechanicalPlanarization (CMP) process may be used to planarize the top surface ofthe PMOS semiconductor layer 112 and the NMOS semiconductor layer 108. ACMP process includes a mechanical component and a chemical component.The mechanical component involves abrasive particles and the chemicalcomponent involves a chemical etchant. In one example, the PMOSsemiconductor layer may include silicon germanium (SiGe). Other types ofsemiconductor materials that are well-suited for PMOS transistors may beused. The silicon germanium may have a concentration of germanium withina range of about 25 to 40%.

To form the fin structures 111, the substrate is patterned usingphotolithographic techniques. For example, a photoresist material may bedeposited and patterned. Patterning the photoresist may be done byexposing the deposited photoresist to a light source through a mask. Thephotoresist layer may then be developed to expose regions that are to beetched. An etching process is then applied to remove portions of thesubstrate to form the fin structures as shown. After the fin structures111 are formed, STI structures may be formed between the fin structures111. This may be done by depositing a dielectric material and etchingthat material to the desired height. The dielectric material and thematerial of the fin structures may be selected so that the dielectricmaterial of the structures can be removed while leaving the finstructures substantially intact.

The method 300 includes a process 304 for forming a dielectric sidewallstructure on the fin structure. The fin sidewall 116 may be depositedthrough use of a deposition process such as a Chemical Vapor Deposition(CVD) process. Other deposition processes may be used to deposit the finsidewall 116. The fin sidewall 116 may include a dielectric materialsuch as a nitride material.

The method 300 further includes a process 306 for forming a gatestructure on the fin structure. In some examples, the gate structure maybe formed before the dielectric sidewall structure is formed. The gatestructure 126 may be formed in one of a variety of manners. In oneexample, a conductive material, such as polysilicon is deposited ontothe substrate. The polysilicon layer is then patterned to createelongated gate structures 126 that wrap around the fin structures 111.After the gate structure is formed, and before the source/drain regions124 are formed, the gate sidewalls 128 may be deposited onto thesidewalls of the gate structure. The gate sidewalls 128 may be adielectric material.

The method 300 further includes a process 308 for etching an upperportion of the sidewall structure. The etching process may be ananisotropic process such as a dry etching process. A dry etching processinvolves directing ions at a substrate to remove material from thatsubstrate. A dry etching process can be selective so as to remove sometype of materials while leaving other types of materials substantiallyintact. Thus, the etching process 120 can remove the fin sidewalls 116while leaving the PMOS fin structures 111 substantially intact. Theetching process 120 may be applied until the top surfaces of the finsidewalls are at a point that is within the middle of the height of thefin structures 111. In some examples, the etching process 120 may beapplied until the top surfaces of the fin sidewalls 116 are abouthalfway between the top surface and bottom surface of the PMOS finstructures 111.

The method 300 further includes a process 310 for performing a plasmadoping process on the fin structure, the plasma doping processintroducing a dopant into the fin structure and the sidewall structure.The plasma doping process may be applied before etching the upperportion of the sidewall structure, after etching the upper portion ofthe sidewall structure, or both. The doping process 118 also introducesthe p-type dopant into the fin sidewall 116. A plasma doping processinvolves using a high voltage direct current (DC) to extract ions fromplasma and inject them into a target. For example, a plasma gas mayinclude p-type dopants such as boron. Such a plasma gas may then beintroduced into a chamber that also includes the substrate. Anelectromagnetic field can then be applied to direct ions from the plasmainto the surface.

The method 300 further includes a step 312 for forming source/drainregions adjacent the gate structure such that a bottom portion of thesource/drain regions corresponds to a top surface of the sidewallstructure. The source/drain regions 124 may be formed by etchingportions of the fin structure to create a cavity within the finstructures. The etching process may be designed so as to create thecavity at a specific depth within the fin structures 111. For example,and as illustrated, the cavity may have a depth that extends abouthalfway through the height of the fin structures 111. After the cavityis formed, an epitaxial growth process may be applied to epitaxiallygrow the source/drain regions 124 within the cavities. The source/drainregions 124 may also be doped in situ. In other words, the source/drainregions 124 may be implanted with the desired dopant species while thesource/drain regions 124 are being formed.

The source/drain regions 124 may include the same type of semiconductormaterial (e.g., silicon germanium) as the PMOS fin structure 111. Insome examples, however, the source/drain regions may have a largerconcentration of germanium than the PMOS fin structure 111. For example,the source/drain regions 124 may have a concentration of germaniumwithin a range of 45-75 percent. Thus, the source/drain regions 124 mayhave a higher concentration of germanium than the channel region 130 andthe under-region 132. In some example, a concentration of germaniumwithin a channel region of the fin structure is within a range of 25-40percent.

In some examples, a concentration of germanium within the source/drainregion is greater than a concentration of germanium within a channelregion. In some examples, the lower portion of the fin structure belowthe source/drain region includes the p-type dopant at a lowerconcentration than the source/drain region. Thus, if the p-type dopantis boron, then the fin structure below the source/drain region will havea lower concentration of boron than the concentration of boron withinthe source/drain regions. In some examples, a bottom of the source/drainregion is positioned at about a halfway point between the top and bottomof the fin structure.

According to one example, a semiconductor device includes a dopedsemiconductor layer and a fin structure disposed on the dopedsemiconductor layer, the fin structure being doped with a p-type dopant.The semiconductor device further includes a source/drain portiondisposed within an upper portion of the fin structure and a fin sidewall formed along a lower portion of the fin structure, the fin sidewallhaving the p-type dopant.

According to one example, a semiconductor device includes a finstructure having an upper portion and a lower portion and a source/drainregion formed within the upper portion, the source/drain regioncomprising a p-type dopant having a first concentration. Thesemiconductor device further includes an under-region positioned withinthe lower portion and aligned with the source/drain region, theunder-region comprising the p-type dopant at a second concentration thatis less than the first concentration. The semiconductor device furtherincludes a fin sidewall formed along the lower portion of the finstructure.

According to one example, a method includes forming a fin structure on adoped semiconductor layer, forming a dielectric sidewall structure onthe fin structure, forming a gate structure on the fin structure,etching an upper portion of the sidewall structure, performing a plasmadoping process on the fin structure, the plasma doping processintroducing a dopant into the fin structure and the sidewall structure,and forming source/drain regions adjacent the gate structure such that abottom portion of the source/drain regions corresponds to a top surfaceof the sidewall structure.

The foregoing outlines features of several embodiments so that thoseskilled in the art may better understand the aspects of the presentdisclosure. Those skilled in the art should appreciate that they mayreadily use the present disclosure as a basis for designing or modifyingother processes and structures for carrying out the same purposes and/orachieving the same advantages of the embodiments introduced herein.Those skilled in the art should also realize that such equivalentconstructions do not depart from the spirit and scope of the presentdisclosure, and that they may make various changes, substitutions, andalterations herein without departing from the spirit and scope of thepresent disclosure.

What is claimed is:
 1. A method for fabricating a semiconductor device,the method comprising: forming a doped semiconductor layer on asubstrate; forming a fin structure on the doped semiconductor layer, thefin structure being doped with a p-type dopant; forming a source/drainregion within an upper portion of the fin structure; and forming a finsidewall along a lower portion of the fin structure, the fin sidewallhaving the p-type dopant.
 2. The method of claim 1, wherein the dopedsemiconductor layer comprises an n-well.
 3. The method of claim 1,wherein the fin structure comprises silicon germanium.
 4. The method ofclaim 1, wherein a concentration of germanium within the source/drainregion is greater than a concentration of germanium within a channelregion.
 5. The method of claim 1, wherein the lower portion of the finstructure below the source/drain region comprises the p-type dopant at alower concentration than the source/drain region.
 6. The method of claim1, wherein the p-type dopant comprises boron.
 7. The method of claim 1,further comprising forming a gate structure on the fin structureadjacent the source/drain region.
 8. The method of claim 1, wherein abottom of the source/drain region is positioned at about a halfway pointbetween a top and a bottom of the fin structure.
 9. The method of claim1, wherein a concentration of germanium within the source/drain regionis within a range of about 45-75 percent.
 10. A method of fabricating asemiconductor device, the method comprising: forming a fin structurehaving an upper portion and a lower portion comprising an under-regioncomprising a p-type dopant at a first concentration; forming asource/drain region within the upper portion, the source/drain regionaligned with the under-region and comprising a p-type dopant having asecond concentration that is less than the first concentration; andforming a fin sidewall formed along the lower portion of the finstructure.
 11. The method of claim 10, wherein a height of the finstructure is within a range of about 50-60 nanometers.
 12. The method ofclaim 10, wherein a height of the fin sidewall is within a range ofabout 5-20 nanometers.
 13. The method of claim 10, wherein aconcentration of germanium within a channel region of the fin structureis within a range of 25-40 percent.
 14. The method of claim 10, whereina concentration of germanium within the source/drain region is within arange of about 45-75 percent.
 15. The method of claim 10, wherein aconcentration of the p-type dopant within the source/drain region iswithin a range of about 3×10²⁰-7×10²⁰.
 16. The method of claim 10,wherein the fin structure is disposed on an n-well.
 17. The method ofclaim 10, wherein the sidewall includes the p-type dopant.
 18. A methodcomprising: forming a fin structure on a doped semiconductor layer;forming a dielectric sidewall structure on the fin structure; forming agate structure on the fin structure; etching an upper portion of thesidewall structure; performing a plasma doping process on the finstructure, the plasma doping process introducing a dopant into the finstructure and the sidewall structure; and forming source/drain regionsadjacent the gate structure such that a bottom portion of thesource/drain regions corresponds to a top surface of the sidewallstructure.
 19. The method of claim 18, wherein the plasma doping processis performed before etching the upper portion of the sidewall structure.20. The method of claim 18, wherein the plasma doping process isperformed after etching the upper portion of the sidewall structure.